[Qemu-devel] [PATCH 2/4] target-arm: Support v6 barriers in linux-user mode

[Peter Maydell <peter.maydell@linaro.org>]

ARMv6 implemented various operations as special cases of cp15 accesses
which are true instructions in v7; this includes barriers (DMB, DSB, ISB).
Catch this special case at translate time, so that it works in linux-user
mode (which doesn't provide a functional get_cp15 helper) as well as
system mode.

Includes minor cleanup of the existing cases (single switch statement,
and doing the "OK in user mode?" test explicitly rather than hiding it in
cp15_user_ok()).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target-arm/translate.c |   51 +++++++++++++++++++++++++++++++----------------
 1 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/target-arm/translate.c b/target-arm/translate.c
index 34d5e6e..c7961b8 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -2498,12 +2498,6 @@ static int cp15_user_ok(CPUState *env, uint32_t insn)
         if (op == 2 || (op == 3 && (insn & ARM_CP_RW_BIT)))
             return 1;
     }
-    if (cpn == 7) {
-        /* ISB, DSB, DMB.  */
-        if ((cpm == 5 && op == 4)
-                || (cpm == 10 && (op == 4 || op == 5)))
-            return 1;
-    }
     return 0;
 }
 
@@ -2579,39 +2573,60 @@ static int disas_cp15_insn(CPUState *env, DisasContext *s, uint32_t insn)
         /* cdp */
         return 1;
     }
-    if (IS_USER(s) && !cp15_user_ok(env, insn)) {
-        return 1;
-    }
-
-    /* Pre-v7 versions of the architecture implemented WFI via coprocessor
-     * instructions rather than a separate instruction.
+    /* We special case a number of cp15 instructions which were used
+     * for things which are real instructions in ARMv7. This allows
+     * them to work in linux-user mode which doesn't provide functional
+     * get_cp15/set_cp15 helpers, and is more efficient anyway.
      */
-    if ((insn & 0x0fff0fff) == 0x0e070f90) {
+    switch ((insn & 0x0fff0fff)) {
+    case 0x0e070f90:
         /* 0,c7,c0,4: Standard v6 WFI (also used in some pre-v6 cores).
          * In v7, this must NOP.
          */
+        if (IS_USER(s)) {
+            return 1;
+        }
         if (!arm_feature(env, ARM_FEATURE_V7)) {
             /* Wait for interrupt.  */
             gen_set_pc_im(s->pc);
             s->is_jmp = DISAS_WFI;
         }
         return 0;
-    }
-
-    if ((insn & 0x0fff0fff) == 0x0e070f58) {
+    case 0x0e070f58:
         /* 0,c7,c8,2: Not all pre-v6 cores implemented this WFI,
          * so this is slightly over-broad.
          */
-        if (!arm_feature(env, ARM_FEATURE_V6)) {
+        if (!IS_USER(s) && !arm_feature(env, ARM_FEATURE_V6)) {
             /* Wait for interrupt.  */
             gen_set_pc_im(s->pc);
             s->is_jmp = DISAS_WFI;
             return 0;
         }
-        /* Otherwise fall through to handle via helper function.
+        /* Otherwise continue to handle via helper function.
          * In particular, on v7 and some v6 cores this is one of
          * the VA-PA registers.
          */
+        break;
+    case 0x0e070f3d:
+        /* 0,c7,c13,1: prefetch-by-MVA in v6, NOP in v7 */
+        if (arm_feature(env, ARM_FEATURE_V6)) {
+            return IS_USER(s) ? 1 : 0;
+        }
+        break;
+    case 0x0e070f95: /* 0,c7,c5,4 : ISB */
+    case 0x0e070f9a: /* 0,c7,c10,4: DSB */
+    case 0x0e070fba: /* 0,c7,c10,5: DMB */
+        /* Barriers in both v6 and v7 */
+        if (arm_feature(env, ARM_FEATURE_V6)) {
+            return 0;
+        }
+        break;
+    default:
+        break;
+    }
+
+    if (IS_USER(s) && !cp15_user_ok(env, insn)) {
+        return 1;
     }
 
     rd = (insn >> 12) & 0xf;
-- 
1.7.1